The present invention relates to leak detection apparatus for pipe couplings where an improved sleeve means is provided which will reduce the testing time, improve the accuracy heretofore attained in such tests, provide for calculation of leak rate, and allow certain safety procedures to be followed.
In the past, a number of arrangements for leak detection in pipe joints has been proposed and used with varying degrees of success. With the increasing depth of wells, both on and off shore, the pressure to which joints are exposed and for which they must be tested has also increased. Further, the ever mounting costs involved in drilling new wells has required significantly increased sensitivity to leakages down to and including approximately 10.sup.-6 cc/sec.
For some time, it has been known that certain trace contents of a well product where even minute leakage is present will, over time, eventually destroy a pipe string by enlarging the leak until unacceptable pressure loss results.
In carrying out pipe and pipe joint leak testing, it is the usual practice to insert into the pipe a packer assembly such as that disclosed in U.S. Pat. No. 3,038,542, the disclosure of which is hereby incorporated by reference and relied upon. The packer assembly includes at least two spaced packer members that are located on either side of a joint to be tested and then expanded to form a closed volume which sets astride the coupling on the inside of the pipe string. A gas under high pressure is fed to this volume with the pressure being in the neighborhood of or in excess of the estimated operating pressure of the well. Various techniques are available for detecting a leak including sensing any pressure drop in the closed volume defined by the packer assembly and the interior of the pipe joint.
In a more recent development, a test operator places a sleeve or collar about the exterior of the pipe joint and employs a mass spectrometer or other instrument to detect a specific gas fed to the interior of the pipe through a packer assembly at high pressure. One frequently used gas is helium mixed with another non-flammable gas such as nitrogen. In many cases, however, these tests have consumed a great deal of time and have not been accurate enough to detect small leaks, as for example 10.sup.-5 -10.sup.-6 cc/sec. In some cases tests have not been carried out at well operating pressures, which can be in excess of 10,000 psi, and at times in excess of 15,000 psi.
Since a single defective coupling can often result in the necessity of pulling up an entire string, it is extremely important that the test of each coupling be carried out correctly and reliably. Yet it is also important that the testing on each coupling be carried out expeditiously and safely at the expected operating pressure so as not to unnecessarily delay the installation of the pipe string.
The present invention satisfies the foregoing criteria and overcomes certain disadvantages of the prior art devices.
According to the present invention, the testing apparatus includes, in one embodiment, a stiff deformable polyurethane or other polymer sleeve which is dimensioned to closely fit over the exterior of a pipe coupling. The conventional coupling includes two threaded pipe ends which are each threaded with a coupling sleeve from opposing ends of the pipe to be joined. The testing sleeve of the present invention has an interior surface shaped to define a small volume at each end of the coupling sleeve. The volume provided at each end of the coupling sleeve is relatively small and may be between 5 and 300 cc and, preferably, is approximately 10 cc.
The polyurethane testing sleeve is formed with a slit running parallel to its longitudinal axis, thereby forming two parallel edges each of which is reinforced by an embedded metal strip and each of which has anchored to each strip a frame member which, in turn, carries an arm. The arms are held by the test operator to facilitate opening the sleeve to install or remove the sleeve from a pipe coupling.
In another embodiment, a stretchable fabric web is provided with a gas impervious layer such as rubber sheet. In use, the web is tightly wrapped around a coupling and secured in place with a "Velcro" fastener. With this arrangement, due to the resiliency of the fabric and rubber sheet layer, a minimum contained volume will be assured while installation and removal of the fabric web can be done very rapidly.
In order to provide an increased concentration of leaked gas, a delay time is introduced prior to sampling the minimum contained volume after pressure is applied inside the pipe being tested.
Utilizing the delay time, contained volume and gas concentration found in the contained volume, leak rate can be calculated.